1 sec vs 10 sec theodolite 1

[ChipN]

What is the accuracy difference between a 1 second vs a 10 second theodolite. I'll be locating trees on a 1 acre tree farm.

 

[IRstuff]

Depends on the distance involved.

1 second at 100 ft is about 0.006 inches



TTFN

Eng-Tips Policies FAQ731-376

 

[ChipN]

Is there a formula that I can use.1 second at 300 feet is about how many inches?Thanks.

 

[CarlB]

The accuracy is approximately the tangent of the angle times the distance. Call the accuracy "delta", then

Delta=Distance x tan (angle)

For 300 ft, 1 second:

Delta=300 x tan (1 sec/3600)=0.0015 ft = 0.02 inches

 

[ChipN]

Thanks for the help.Chip

 

[StanBognatz]

For measuring trees, there is no difference in accuracy. Think of it this way - 1 arc-sec = the width of a dime viewed from 1.25 MILES away. So even with 10 arc-sec, you're looking at something the width of 10 dimes, about 5 inches, from 1.25 MILES. So across an acre, you'd be down do the 1/2 dime range or less. And, as usual, your setups and instrument leveling will degrade your readings more than anything.

Oh, and don't forget to use an offset measurement to get the center of tree measurement.